Infectious bursal disease has been observed in chickens since 1957. Infectious bursal disease is caused by a highly contagious double stranded RNA birnavirus, which has been designated infectious bursal disease virus ("IBDV"). IBDV is found where chickens are raised commercially.
Chickens infected with IBDV in serotype I exhibit anorexia, depression, watery diarrhea, ruffled feathers, soiled vent feathers, and vent picking. Highly pathogenic viruses, found outside the United States can cause mortality in 50% or more of affected chickens. Viruses that are not of the highly pathogenic type cause 100% morbidity and can cause up to 5% mortality in chicken. Animals which survive the disease are permanently immunosuppressed and are highly susceptible to other infections and diseases.
Protection of chickens from infectious bursal disease is complicated by the presence of several antigenic types of the virus. Vaccination of chickens with IBDV of one antigenic type does not always protect the vaccinated animals from infection with IBDV of a different antigenic type. Moreover, the currently available vaccines are not able to protect animals against an IBDV that is not a member of one of the known antigenic types.
It is also desirable to have methods for preparing immunogenic compositions that are used to protect chickens from infection with IBDV, particularly from infection with new antigenic forms of IBDV.